1. Field of the Invention
The present invention relates to a method for manufacturing a honeycomb structure, and a honeycomb structure.
2. Discussion of the Background
There has been known, as an exhaust gas-purifying filter or a catalyst supporting carrier, a honeycomb structure formed by combining a plurality of pillar-shaped honeycomb fired bodies each having a large number of cells longitudinally placed in parallel with one another. The honeycomb structure includes a ceramic block formed by the honeycomb fired bodies and a coat layer disposed on the periphery of the ceramic block. The ceramic block is formed by fixing a plurality of the pillar-shaped honeycomb fired bodies to one another by interposing an adhesive layer that is formed on the side surfaces of the honeycomb fired bodies.
As a method for manufacturing the honeycomb structure, there has been known a method in which the adhesive layer and the coat layer are formed in separate steps. In this method, firstly, a plurality of honeycomb fired bodies are bonded to one another with a sealing material paste, and then this sealing material paste is dried and solidified to form an adhesive layer. Thus, a ceramic block formed by the honeycomb fired bodies firmly bonded to one another can be manufactured. Next, a sealing material paste is applied to the periphery of the ceramic block, and then is dried and solidified to form a coat layer. Thus, a honeycomb structure is manufactured.
In the above method, however, the adhesive layer and the coat layer are formed in the separate steps, and as a result, an interface that divides the adhesive layer from the coat layer is formed between the two layers. When such a honeycomb structure is used as, for example, an exhaust-gas purifying filter for vehicles, the honeycomb structure is exposed to rapid increase in temperature at the beginning of driving, experiences long-term repeat of heat cycle from driving of a vehicle and regeneration of the filter, and the like. As a result of this, the honeycomb structure tends to be separated or broken at the interface between the adhesive layer and the coat layer.
WO 2008/126334 A1, WO 2008/139608 A1, and WO 2005/047210 A1 each disclose a method for integrally forming an adhesive layer and a coat layer with no interface that divides the two layers. Specifically, in the methods of WO 2008/126334 A1 and WO 2008/139608 A1, firstly, a plurality of honeycomb fired bodies are combined into a specific shape in such a manner to maintain a constant spacing with one another using an assembling apparatus, and this shape is fixed with a molding frame. Next, a sealing material paste is filled into gaps between the honeycomb fired bodies and a gap between the molding frame and the honeycomb fired bodies. Then, this sealing material paste is dried and solidified, and thus the adhesive layer and the coat layer are integrally formed with no interface that divides the two layers. WO 2005/047210 A1 discloses a method in which upon combining honeycomb fired bodies into a specific shape, the honeycomb fired bodies are kept at regular spaces using a spacing member, and an adhesive layer and a coat layer are integrally formed using a molding frame.
The contents of WO 2008/126334 A1, WO 2008/139608 A1, and WO 2005/047210 A1 are incorporated herein by reference in their entirety.